Gas-generating pyrotechnic monolithic blocks

ABSTRACT

A substantially cylindrical gas-generating pyrotechnical monolithic block has a thickness no lower than 10 mm, an equivalent diameter no lower than 10 mm, and a porosity lower than 5%; and a composition, given as weight percentages, which contains, for at least 94% of the weight thereof: +77.5% to 92.5% of guanidine nitrate, +5% to 10% of basic copper nitrate, and +2.5% to 12.5% of at least one inorganic titanate with a melting temperature higher than 2100 K.

The present invention relates to gas-generating pyrotechnic monolithicblocks (“large” pyrotechnic objects); said blocks being suitable forbeing integrated in devices dedicated for pressurization of structuresof a more or less large volume, depending on the intended application.Said blocks are more particularly suitable for being integrated indevices whose working requires pressurization to be provided over arelatively long period of time, very significantly greater than theperiods of time required for the working of gas generators for airbags(times of at most a few milliseconds) and even of gas generators forhood-lifting jacks (times of about 100 milliseconds).

Owing to their intrinsic size, porosity and composition characteristics,the pyrotechnic monolithic blocks of the invention give particularlygood performance (with reference to specifications with many stringentrequirements). They give particularly good performance notably withrespect to their (low) combustion rate and (low) temperature, their easeof production and their gas yield (see below).

The devices in question are, for example, extinguishers (the gasesrequired for their working are used as propellant gas, serving forexpelling an extinguishing liquid through a nozzle), actuators of jacksfor opening doors in emergency (the gases required for their working areused for operating a jack mechanically), devices for inflating flexiblestructures (the gases required for their working provide deployment andpressurization of a flexible, impervious envelope). The inflation ofthese flexible structures may meet various needs: the need forobstruction of a pipeline (for example, for anti-discharge systems, withthe aim of limiting the risks of pollution in case of industrialaccident), the need to generate flotation bags (for example foremergency ditching, notably of a helicopter), the need to deploy aflexible slide (for example for emergency evacuation of the passengersfrom an aircraft), for example.

To date, the working of such devices, which are therefore generallysafety or emergency devices, is most often provided by the use of aneutral gas (nitrogen, helium, etc.), stored at high pressure (200 to400 bar) in a tank. This technology has advantages, such as the use of aneutral gas (inert), intrinsically nontoxic and moreover cold. However,as it uses a pre-compressed gas, at high pressure, it has notabledisadvantages:

a) the gas storage tanks are still of large dimensions (even though thegas is highly compressed);

b) the presence of gas stored at high pressure in a tank (bottle, etc.)requires, for obvious safety reasons, that said tank is dimensionedobserving the rules of the art and the directives with respect to anenvelope under pressure so as to withstand the high internal pressurefor long periods, which leads to structures either of large thickness(and therefore of considerable weight), or using lightweight materials(composites) with high production cost; finally,

c) periodic operations of maintenance are required to guarantee safe,optimal working throughout the service life of the device. Theseoperations obviously affect the operating costs.

Disadvantages a and b above prove particularly critical for on-boarddevices (notably in the aeronautical sector, in view of the constraintsimposed there in terms of weight and/or dimensions). Elimination ofregular maintenance operations (disadvantage c above) would of courseproduce a very advantageous decrease in operating costs.

The use of solid pyrotechnic objects for the working of devices of theabove type has also been described.

The specifications for the working of such devices require that a volumeof gas, at a moderate temperature, is generated, starting from thepyrotechnic objects in question, relatively slowly and constantly, for arelatively long specified duration, for so pressurizing a structure of amore or less large volume (we may mention, not in any way limiting,volumes of about 1 L (jacks for opening doors, for example), about 3000L (helicopter flotation bags, for example), or even about 20 000 L(evacuation slide, for example)).

Patent application WO 2007/113299 thus describes pyrotechnic objects,intended for generating gas over a relatively long period of time (timesfrom 50 ms to 1 min are mentioned), whose composition, binder-free,contains guanidine nitrate (GN: as reducing charge) and basic coppernitrate (BCN: as oxidizing charge), in a GN/BCN ratio close to thestoichiometric equilibrium. Said composition therefore has an almostequilibrated oxygen balance (close to zero). This endows saidpyrotechnic objects with a combustion temperature and a combustion ratethat are too high with reference to the specifications presently inquestion (see below).

The objects described in said application WO 2007/113299, advantageouslyobtained by a dry compacting method, are of substantially cylindricalshape and have a thickness greater than 5 mm, a diameter greater than orequal to 10 mm (generally thickness and/or diameter between 10 and 60mm) and porosity between 1 and 8%. In fact, low porosities (<5%, andmore advantageously <3%) cannot easily be obtained with the compositionsdescribed (and their densification characteristic), except for objectsof limited size. Now, a person skilled in the art is aware of thecritical nature of this parameter porosity. A “high” porosity value (inthis case above 4-5%) is generally of a nature such as to increase thedispersion of ballistic working of the pyrotechnic object, to give saidpyrotechnic object insufficient durability in environments with severevibrations for prolonged periods and, for this class of pyrotechniccompounds (i.e. based on a GN+BCN mixture), to increase the value of therate of combustion.

Considering their particularly advantageous properties in a context oflong-term gas generation, the pyrotechnic monolithic blocks of theinvention (described below) may be regarded as improvements to thepyrotechnic objects according to the teaching of application WO2007/113299.

The inventors propose gas-generating pyrotechnic monolithic blocks whosecombustion gases replace the pressurized gases of the prior art, forproviding working of safety or emergency devices (more generally forproviding pressurization of structures). This substitution, which isadvantageous per se (see above for the disadvantages of using gas underpressure), is the more so as said blocks of the invention giveparticularly high performance, with reference to stringentspecifications. In any case, they give better performance than theobjects described in application WO 2007/113299.

The main requirements of said specifications are presented below.

In order to deliver, particularly advantageously, a suitable flow rate(flow rate=rate of combustion×surface area undergoing combustion) ofcombustion gas for a relatively long time (generally at least 500 ms andup to 2 min), the inventors investigated:

-   -   large blocks (typically with a thickness ≧10 mm and an        equivalent diameter ≧10 mm), so that their surface area of        combustion is reduced (so that they have a large thickness to be        burnt); said blocks being able to be produced (formed) densified        (i.e. having a low porosity: <5%, advantageously ≦3%, very        advantageously ≦2%), with a limited compacting force, which        constitutes a real advantage. Such blocks allow charges to be        obtained that have a density (the density of a charge        corresponding to the weight of pyrotechnic product relative to        the charge volume occupied) that is as high as possible (in        order to allow a decrease in overall dimensions of the gas        generator, which is particularly beneficial in on-board systems,        notably intended for the aeronautical sector. Typically, this        requirement effectively prohibits the use of charges in the form        of pellets in bulk, such as those used conventionally in gas        generators for airbags). Inhibition (for example, by deposition        of a thermosetting varnish) of the lateral surface of the blocks        may moreover be provided to increase the combustion time of the        blocks, in contexts where a very long pressurization time is        required;    -   blocks having a low combustion temperature: less than or equal        to 1415 K. Such a low combustion temperature limits the        inevitable loss of pressure due to cooling of the gases        generated. This low combustion temperature is moreover        particularly beneficial with reference to the thermal stresses        imposed on the gas generator and on the structure to be        pressurized;    -   blocks having a low rate of combustion. More precisely, the        following are required: 1) a moderate combustion rate at low        pressure (combustion must take place at low pressure (this is        particularly beneficial with reference to the constraints of        pressure resistance of the gas generator (and therefore with        reference to the weight of the latter) and of the structure to        be pressurized) and its rate is typically below 6 mm/s between 1        and 10 MPa (it will be understood that the combustion rate at        high pressure (20 MPa) is potentially above 6 mm/s but said        combustion rate at high pressure is not at all relevant here, in        view of the desired applications (pressurization of large-volume        structures over a long period)); and 2) a nonzero rate at        atmospheric pressure (it is desirable for the blocks to burn        completely);    -   blocks having good characteristics of ignitability and of        combustion warm-up;    -   blocks generating combustion residues in agglomerated form        (residues that are thus easily filterable, advantageously making        it possible to reduce the dimensions of the gas filtration        systems that have to be incorporated in the device);    -   blocks also having good gas yields (generally above 38 mol/kg,        in a preferred variant above 42 mol/kg), making it possible to        limit the weight of pyrotechnic charge to be incorporated and        therefore the weight of the system (this is particularly        advantageous for devices intended for the aeronautical market).

With reference to such specifications, the inventors therefore proposegas-generating pyrotechnic monolithic blocks that are original, withparticularly good performance, and which are characterized by theirsize, porosity and composition.

Said gas-generating pyrotechnic monolithic blocks of the invention, ofsubstantially cylindrical shape (generally, but not exclusively,cylinders of revolution or quasi-cylinders of revolution), combinecharacteristics

a) of size: a thickness greater than or equal to 10 mm and an equivalentdiameter greater than or equal to 10 mm,

b) of porosity: a porosity below 5% (this parameter, expressed inpercentage, corresponds to the ratio of the difference between thetheoretical density and the actual density to the theoretical density),and,

c) of composition: their composition, expressed as percentage by weight,contains, for at least 94% of their weight:

+77.5 to 92.5% of guanidine nitrate (GN),

+5 to 10% of basic copper nitrate (BCN), and

+2.5 to 12.5% of at least one inorganic titanate whose melting point isabove 2100 K.

With reference to the size characteristics stated above, it will beunderstood that the blocks in question consist of large objects. Not inany way limiting, it may be stated here that they generally have athickness between 10 and 100 mm (10 mm≦e≦100 mm) and/or, very generallyand, an equivalent diameter between 10 and 100 mm (10 mm≦φ≦100 mm).According to an advantageous embodiment, they have a thickness between20 and 80 mm (20 mm≦e≦80 mm) and/or, preferably and, an equivalentdiameter between 20 and 80 mm (20 mm≦φ≦80 mm).

With reference to the porosity characteristic stated above, it will beunderstood that the blocks in question are dense blocks. According to anadvantageous embodiment, the porosity of said blocks is less than orequal to 3%. According to a very advantageous embodiment, the porosityof said blocks is less than or equal to 2%, or even less than or equalto 1% (a low (≦2%), or even very low (≦1%) value of porosity is obtained(with the compositions of the blocks of the invention) by application ofa nominally high compression force, and a porosity value that is lesslow but is already low (>2% and <5%) is obtained by application of acompression force that is reduced relative to that required forobtaining an equivalent porosity with the compositions according to theteaching of WO 2007/113299 (see the appended FIGURE)).

A person skilled in the art will already understand the great benefit ofthe blocks of the invention, which combine large size and low porosity.The specific composition of the blocks makes such combination possibleand is particularly beneficial with reference to the combustionparameters of said blocks (see the combustion temperature (≦1415 K) andthe combustion rates (<6 mm/s between 1 and 10 MPa and nonzero atatmospheric pressure) stated in the specifications above).

The composition of the blocks of the invention is a composition thatcontains, for at least 94% of its weight:

-   -   the three ingredients identified above: guanidine nitrate (GN)        as oxidizing charge, basic copper nitrate (BCN) as reducing        charge, and inorganic titanate(s) as refractory charge (the        melting point of this charge (>2100 K) is still above the        combustion temperature of the base GN+BCN in which it is present        (such a base, unbalanced (see below), has a combustion        temperature still below about 1500 K)) providing a dual function        of agent for agglomeration of the solid combustion residues and        of combustion modifier (which makes it possible to reach,        unexpectedly, the severe properties of combustion (temperature        and combustion rates) that are required);    -   in the proportions stated: in a GN+BCN base that is highly        unbalanced with respect to oxygen balance (owing to its weight        ratio GN/BCN ≧7.75, advantageously ≧8.5), this imbalance being        appropriate with reference to the required combustion        properties, the at least one titanate is present, in a        significant amount (≧2.5 wt. %, ≧5 wt. % according to one        embodiment, so that the technical effect of optimization on the        combustion properties that it develops (unexpectedly) is        significant) but not excessive (≦12.5 wt. %, quite particularly        with reference to the gas yield and ignitability).

With reference to the composition of the blocks of the invention, moreparticularly the GN+BCN base of said composition, the following may beadded.

1) The high content of guanidine nitrate in the compositions of theblocks of the invention (from 77.5 to 92.5 wt. %) is particularlyadvantageous, with reference to the density (to the low porosity) ofsaid blocks, owing to the rheoplastic behavior of said guanidinenitrate. It is particularly advantageous for implementing step(s) ofcompacting and/or compression during preparation of said blocks, notablyby a dry process (see below).

2) Guanidine nitrate and basic copper nitrate are therefore present in aweight ratio R=GN/BCN (unbalanced) between 7.75 and 18.5 (see the weightratios stated for GN and BCN). Said weight ratio is advantageouslybetween 8.5 and 15, very advantageously between 8.5 and 12, andespecially preferably between 8.5 and 10. These embodiments that areadvantageous, very advantageous and particularly preferred are so withreference to the required combustion properties but also with referenceto the ignitability and gas yield of the blocks in question.

With reference to the at least one inorganic titanate present in thecomposition of the blocks of the invention, the following may be added.

Said at least one inorganic titanate is preferably selected from themetal titanates and the alkaline-earth titanates (=the metal titanates,the alkaline-earth titanates and mixtures thereof). The composition ofthe blocks of the invention thus very advantageously contains a metaltitanate or an alkaline-earth titanate. Preferably, the composition ofthe blocks of the invention contains strontium titanate (SrTiO₃, whosemelting point is 2353 K) and/or calcium titanate (CaTiO₃, whose meltingpoint is 2248 K) and/or aluminum titanate (Al₂TiO₅, whose melting pointis 2133 K). Especially preferably, it contains strontium titanate(SrTiO₃), calcium titanate (CaTiO₃) or aluminum titanate (Al₂TiO₅).

The dual function of said titanates in the composition of the blocks ofthe invention should be emphasized. Said titanates perform the role ofagglomerating agent of the combustion residues (owing to theirrefractory nature (melting point >2100 K), they conserve their physicalstate of pulverulent solid (they are obviously used in this form) at thecombustion temperature of the block, hence agglomeration of the copperresidues (residues in (wholly or partly) liquid form at the combustiontemperature of the composition) generated during combustion of BCN) and,present within a GN+BCN base that is highly unbalanced in oxygenbalance, they make it possible to obtain, surprisingly, the specificcombustion properties that are required (a combustion temperature lessthan or equal to 1415 K, a moderate rate of combustion, less than orequal to 6 mm/s, at low pressure (between 1 and 10 MPa) and a nonzerocombustion rate at atmospheric pressure), combustion properties that arenecessary for the intended functional need of pressurization, over along time (times from 500 ms to 2 min were stated above), of more orless large volumes (volumes from 1 L to 20 000 L were mentioned above).Their use seems particularly appropriate with reference to the nonzerocombustion rate at atmospheric pressure.

The three essential constituents of the blocks of the inventionidentified above—GN+BCN+at least one inorganic titanate whose meltingpoint is above 2100 K—therefore represent at least 94 wt. % of the totalweight of said blocks. They might perfectly well represent at least 97%of the latter, at least 99% of the latter, or even 100% of the latter.

In addition to said three essential constituents of the blocks of theinvention, the composition of said blocks may contain other ingredients.It is to be understood that said other ingredients should only bepresent at most at a rate of 6 wt. % and, obviously, only if theirpresence does not significantly affect the required properties, quiteparticularly of combustion. Said other ingredients are, not exclusively,but generally, selected from processing additives (manufacturing aids),binders and fluxes (see below).

According to a first variant, the composition of the blocks of theinvention contains, besides said three essential constituents, at leastone processing additive (manufacturing aid, consisting for example ofcalcium stearate or graphite). Said processing additive is generallypresent at a content not exceeding 1 wt. %. Conventionally it is presentat a content not exceeding 0.5 wt. %. Its presence is particularlyappropriate for obtaining the blocks of the invention by dry processing(see below).

In the context of this first variant, the composition of the blocks ofthe invention advantageously comprises 100 wt. % of said guanidinenitrate, basic copper nitrate, at least one inorganic titanate and atleast one processing additive. The blocks of the invention that havethis advantageous composition are generally obtained by dry processing.However, they may also be obtained by wet processing, quite particularlyby wet processing comprising a spraying step (see below).

According to a second variant, the composition of the blocks of theinvention contains, besides said three essential constituents (and,optionally, in addition, said at least one processing additive), atleast one binder (for example of cellulosic or acrylic type) or at leastone flux (for example of the alkali metal chloride salt type, such asNaCl or KCl). The presence of at least one such binder may notably besuitable for obtaining blocks of the invention by extrusion, optionallyby a wet method (the binder then contributing to the formation of a gelon contact with the solvent used (water being the preferred “solvent”)(see below)); the presence of at least one such flux may notably besuitable for obtaining blocks of the invention by dry processing (seebelow), quite particularly for obtaining blocks formulated fromcompositions characterized by a very low combustion temperature. Said atleast one such binder or at least one such flux is generally present ata content not exceeding 5 wt. %, very generally present at a content notexceeding 3 wt. %.

In the context of this second variant (and also in that of the firstvariant above), the composition of the blocks of the inventionadvantageously comprises 100 wt. % of said guanidine nitrate, basiccopper nitrate, at least one inorganic titanate, at least one processingadditive and at least one binder or at least one flux. It veryadvantageously comprises 100 wt. % of said guanidine nitrate, basiccopper nitrate, at least one inorganic titanate, at least one processingadditive and at least one flux. The blocks of the invention that havethis very advantageous composition are generally obtained by dryprocessing.

Whatever their precise characteristics—thickness and diameter above 10mm, porosity below 5% and composition constituted to at least 94 wt. %of guanidine nitrate, basic copper nitrate and at least one inorganic(refractory) titanate, present in the proportions stated—the blocks ofthe invention may, on at least one part of their surface, be inhibitedagainst combustion (covered with a layer of suitable material(combustion inhibiting material), which is generally in the form of a(incombustible) varnish). Such inhibition is a conventional means(notably described in patent application FR 2 275 425 and U.S. Pat. No.5,682,013) that makes it possible to slow their combustion (already“intrinsically” slow) and therefore obtain very long combustion times(see the 2 min stated above).

On reading the foregoing, a person skilled in the art will appreciatethe benefits of the blocks of the invention, whose characteristics ofsize, porosity and composition enable them to satisfy the stringentrequirements of the specifications presented above. In support of thisassertion, we may consider the results stated in the examples hereunder.

The blocks of the invention may be obtained by conventional methods, bya wet process or a dry process. It is to be understood that the originalcomposition of said blocks accounts for their advantageous properties,and also allows them to be obtained in advantageous conditions.

The blocks of the invention are advantageously obtained by a dryprocess. The high content of guanidine nitrate in their composition wasemphasized above.

Such a dry process may roughly be summarized as a compression of thepulverulent mixture obtained by mixing the constituents of the blocks(three essential constituents and optionally, in addition, at least oneother ingredient; advantageously, three essential constituents+at leastone processing additive and optionally at least one flux), saidingredients being used, conventionally, in the pulverulent state. Thepressure applied on the pulverulent mixture arranged in a suitable moldis generally between 10⁸ and 6.5×10⁸ Pa.

Such a dry process may comprise several steps, which were notablydescribed in patent application WO 2006/134311. The first step is a stepof (dry) compacting of a mixture of some powdered constituents or of thepowdered constituents of the blocks (all the constituents(advantageously, the three essential constituents+at least oneprocessing additive and optionally at least one flux) may be mixed orall except the at least one titanate (therefore advantageously,GN+BCN+at least one processing additive and optionally at least oneflux) (see below)). Dry compacting is generally carried out, in a mannerknown per se, in a roll compactor, at a compacting pressure between 10⁸and 6.10⁸ Pa. At the end of said compacting step, it is so generallyobtained a flat plate (when two rolls with a flat surface are used) or aplate with protuberances (when one of said rolls used has a surface withrecesses). The second step is a step of granulation of the compactedmaterial obtained (therefore generally a flat plate or a plate withrecesses). The granules obtained generally have a grain size (a mediandiameter) between 200 and 1000 μm (as well as an apparent densitybetween 0.7 and 1.2 g/cm³). The third step is a (dry) compression step(=shaping step) of the granules obtained. The pressure applied isgenerally between 10⁸ and 6.5×10⁸ Pa. The at least one titanate ispresent with the other constituents of the blocks of theinvention—GN+BCN mainly, or even exclusively—i.e. at the start of themethod for manufacturing the blocks of the invention, or is added,further downstream in the manufacturing method, to the granules, beforecarrying out compression. It would not be ruled out completely for it tobe added in several times, at the start (to the mixture of powders) andfurther downstream (to the granules).

The (conventional) dry processes described above are employed, in thecontext of the present invention, to obtain blocks that have thecharacteristics of composition, size and porosity explained above (i.e.notably a thickness to be burnt greater than or equal to 10 mm,generally between 10 and 100 mm, advantageously between 20 and 80 mm).

In this context of obtaining blocks of the invention by a dry process,the guanidine nitrate (GN) and basic copper nitrate (BCN) used (in theform of powder) advantageously have a fine grain size (value of themedian diameter), less than or equal to 20 μm. Said grain size isgenerally between 1 and 20 μm. These are in fact conventional grainsizes.

The blocks of the invention may also be obtained by a wet process.

According to one variant, said wet process comprises extruding a pastecontaining all the constituents of the block (advantageously, guanidinenitrate, basic copper nitrate, the at least one titanate, at least oneprocessing additive and at least one binder) and a solvent (water beingthe preferred “solvent”).

According to another variant, said wet process comprises:

a) a step of preparing an aqueous solution of at least one of theessential constituents (generally of at least the reducing charge: GN)and optionally of preparing a suspension of at least one other of saidessential constituents that is not soluble (generally of at least theoxidizing charge: BCN) in said solution, thenb) obtaining a powder from said solution or suspension by spray-drying,optionally c) adding, to said powder, the constituent or constituentsthat was/were not previously put in solution or suspension (on theassumption that all the ingredients were not), finallyd) shaping the pulverulent mixture thus obtained (=powder obtained atthe end of spray-drying or powder obtained at the end of spray-dryingadded with said complementary constituent or constituents=powdercontaining all the constituents of the required block) for generating ablock;said at least one inorganic titanate being added to the solution orsuspension to be spray-dried (atomized) and/or to the spray-dried(atomized) powder (before it is shaped).

The shaping of the pulverulent mixture is generally a conventionalcompression (by a known dry compression method). Compression pressuresfrom 10⁸ to 6.5×10⁸ Pa were stated above, but are not in any waylimiting.

The (conventional) wet processes stated above are employed in thecontext of the present invention to obtain blocks that have thecharacteristics of composition, size and porosity explained above (i.e.notably a thickness to be burnt greater than or equal to 10 mm,generally between 10 and 100 mm, advantageously between 20 and 80 mm).

According to another of its aims, the present invention relates to gasgenerators containing a gas-generating solid pyrotechnic charge.Characteristically, the gas generators of the invention contain a chargethat contains at least one block (gas-generating pyrotechnic monolithicblock, of substantially cylindrical shape) of the invention and/or asobtained by the methods reviewed above. Such generators, integrating apyrotechnic charge containing several blocks of the invention, in anordered configuration (for example in the form of a stack of severalblocks), as opposed to a bulk charge, said (stacks of) blocks beingfurthermore able to be inhibited on their lateral surface, are quiteparticularly suitable for pressurization of structures for long, or evenvery long periods (note the 500 ms to 2 min stated above).

It is now proposed to illustrate the invention, not in any way limiting.

I. Table 1 below presents 8 examples (Ex. 1 to Ex. 8) of composition ofblock of the present invention as well as the characteristics of saidcompositions evaluated by means of calculations, notably thermodynamic.

These compositions and their characteristics are to be compared withthose of examples A, B and C, given for comparison:

-   -   the composition in example A is a composition according to the        teaching of WO 2007/113299. It contains 52.44 wt. % of GN and        44.87 wt. % of BCN (ratio R=GN/BCN (=1.2) is close to the        stoichiometric equilibrium). It also contains 2.69 wt. % of        alumina (slagging agent (according to WO 2007/113299));    -   the composition in example B is a composition “according to the        teaching of WO 2007/113299” (see its contents of GN and BCN,        close to the stoichiometric equilibrium (R=1.2)) which further        contains 4 wt. % of strontium titanate;    -   the composition in example C is an unbalanced GN+BCN base        composition (R=GN/BCN=8.7). Besides GN and BCN, said composition        contains alumina (slagging agent) at a level identical to that        of the composition of example A.

The compositions of said examples A, B and C have combustiontemperatures above 1415 K.

It is noted that the presence of strontium titanate in a compositionhaving an almost equilibrated oxygen balance (close to zero) has hardlyany effect on the combustion temperature (see the values of saidcombustion temperature for the compositions in examples A (1905 K) and B(1889 K)).

The combustion temperature of the composition in example C (1438 K) isstill above 1415 K.

The compositions in examples 1 to 8 of the invention contain,characteristically, guanidine nitrate (GN) and basic copper nitrate(BCN), in an unbalanced weight ratio (greater than or equal to 8.5), aswell as an inorganic titanate at a percentage by weight greater than orequal to 3% and less than or equal to 12.5%.

The characteristics of the compositions of examples 1 to 8 in Table 1show that adding strontium titanate (SrTiO₃) or calcium titanate(CaTiO₃) to a composition based on GN+BCN that is highly unbalanced inoxygen balance (of the type in example C) makes it possible to obtain alow value of combustion temperature (below the threshold of 1415 Kstipulated in the specifications (see above)) while maintaining a highgas yield (greater than or equal to 39.5 mol/kg).

Regarding the rates of combustion, reference may be made to paragraph IIbelow.

TABLE 1 Examples Ex. A Ex. B Ex. C Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6Ex. 7 Ex. 8 Ingredients Guanidine Nitrate (GN) % 52.44 52 87.31 85 82.780.3 85 82.7 80.3 78.2 86.9 Basic Copper Nitrate (BCN) % 44.87 44 10 9.89.6 9.5 9.8 9.6 9.5 9.1 9.9 Alumina (Al₂O₃) % 2.69 — 2.69 — — — — — — —Ca Stearate % — — — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Strontium titanate(SrTiO₃) % — 4 — 5 7.5 10 — — — — 3 Calcium titanate (CaTiO₃) % — — — —— — 5 7.5 10 12.5 Characteristics Weight ratio (R) GN/BCN 1.2 1.2 8.78.7 8.6 8.5 8.7 8.6 8.5 8.6 8.8 Oxygen balance % −3.3 −3.3 −20.5 −20.4−19.8 −19.1 −20.4 −19.7 −19.0 −18.5 −20.9 Combustion temperature K 19051889 1438 1398 1377 1358 1411 1396 1382 1364 1414 Density g/cm³ 1.992.01 1.55 1.58 1.61 1.64 1.58 1.60 1.63 1.66 1.56 Gas yield mol/kg 29.529.2 43.7 42.8 41.6 40.5 42.8 41.6 40.5 39.5 43.8 at 1bar - 1000 K

II. The combustion rates of blocks of the invention were compared withthose of blocks according to the teaching of WO 2007/113299.

In fact:

-   -   the combustion rates measured at 2 MPa and at 0.1 MPa were        measured on blocks (with a diameter: 24.6 mm and a thickness:        10 mm) having, respectively, the composition of example 8        according to the invention and the composition of example A        (according to WO 2007/113299) in Table 1 above, and    -   the combustion rates at 20 MPa (high pressure) were measured on        pellets (with a diameter: 6.35 mm and a thickness: 2 mm) having,        respectively, the composition of example 8 according to the        invention and the composition of example A (according to WO        2007/113299) in Table 1 above. This is purely a suitable        geometry for measuring the combustion rate at high pressure.

The blocks and pellets were obtained by the same dry process(compacting+granulation+compression), carried out in the same conditions(notably the same compacting and compression pressure), so that thecombustion rates measured are comparable.

These measured combustion rates are presented in Table 2 below.

The porosities of said blocks and pellets obtained in said sameconditions are stated below:

Block Pellet Ex. A 4.5% 4.0% (porosities above 3%) Ex. 8 1.5% 0.5%(porosities below 3%)

TABLE 2 Examples Characteristics Ex. A Ex. 8 Combustion rate at 10 MPamm/s 16 5 Combustion rate at 2 MPa mm/s 8 2 Combustion rate at 0.1 MPamm/s 1 0.4 Agglomerated appearance of the — yes yes combustion residues(in the form of a skeleton of the pyrotechnic block)

The above results show that the pyrotechnic block according to theinvention has combustion rates (at 2 MPa and at 0.1 MPa) that are verysignificantly lower than those of the block of the prior art. The sameapplies to the rate of combustion, at 10 MPa, measured on the pellets.

Moreover, it was found that the block according to the invention,despite the considerable imbalance of the GN/BCN ratio in itscomposition, advantageously displays self-sustaining combustion up tothe minimum value desired (i.e. up to atmospheric pressure).

III. In the following, the densification characteristics of thecompositions of the blocks of the invention are now considered. Thesedensification characteristics are significantly improved relative tothose of the compositions according to the teaching of WO 2007/113299.These densification characteristics notably allow the obtaining ofblocks with very low porosity (<5%, advantageously ≦3%, veryadvantageously ≦2%, or even ≦1%).

The accompanying FIG. 1 shows the densification curves (i.e. thevariation of the porosity value as a function of the pressure applied onthe material during a compression step), measured in comparison with thecomposition in example 1 (Ex. 1) according to the invention and with thecomposition of comparative example A (Ex. A) (according to the teachingof WO 2007/113299). These densification curves were established in acontext of manufacture of pellets (dry process:compacting+granulation+compression), with different values of thecompression force. The value of compression force applied is thentranslated into an equivalent value of material pressure according tothe following equation: Material pressure (in bar; abscissa)=compressionforce applied (in N) divided by the surface area of the imprint of thecompression punch (in m²) divided by 10⁵. The porosity value (ordinate)is calculated from measurement of the dimensions (thickness, diameter)and weight of the pellet (tablet) obtained (it is expressed as apercentage; it corresponds to the difference between the theoreticaldensity value and the measured density value, relative to thetheoretical density value (see above)).

For values of pressure above 3000 bar, the composition according toexample 1 of the invention allows pellets to be obtained, characterizedby a porosity value less than or equal to 1%, i.e. very close to themaximum densification. For one and the same value of pressure applied(3000 bar), the measured porosity value for pellets according to theprior art is significantly higher (of the order of 5%).

A person skilled in the art knows that it is advantageous to be able tolimit the compression force, as this contributes favorably to reducingthe mechanical stresses (fatigue, wear) applied on the tooling. Thiscompression force is greater for larger dimensions of the object to becompressed. In the context of the present invention, the manufacture ofmonolithic blocks of large diameter (for example 38 mm) and withthickness of 20 mm (such as is required for certain intendedapplications) then requires applying a high compression force in orderto guarantee the obtaining of a value of densification as close aspossible to the maximum theoretical density value.

According to the curves in FIG. 1, the obtaining of a porosity valueless than or equal to 4% for the composition according to comparativeexample A requires a high value of material pressure, of the order of4000 bar, that is to say an equivalent compression force of the order of45 tonnes. In comparison, a porosity value less than or equal to 4% (orpreferably less than or equal to 3%) for the composition according tothe invention (example 1) is obtained for a significantly lower value ofmaterial pressure, of the order of 1000 bar (1500 bar), that is to sayan equivalent compression force of the order of 11 tonnes (17 tonnes).Thus, the composition according to example 1 of the present inventionadvantageously makes it possible either to reduce the compression forcesignificantly (for one and the same intended level of porosity), orobtain a lower value of porosity (for one and the same level ofcompression force applied).

These advantageous characteristics of densification shown on pellets areof course transposable to blocks (of the invention).

1. A gas-generating pyrotechnic monolithic block, of substantiallycylindrical shape, wherein: the gas-generating pyrotechnic monolithicblock has a thickness greater than or equal to 10 mm, an equivalentdiameter greater than or equal to 10 mm, and a porosity below 5%; andwherein a composition of the gas-generating pyrotechnic monolithicblock, expressed in percentage by weight, contains, for at least 94% ofits weight: +77.5 to 92.5% of guanidine nitrate, +5 to 10% of basiccopper nitrate, and +2.5 to 12.5% of at least one inorganic titanatewhose melting point is above 2100 K.
 2. The block as claimed in claim 1,whose thickness is between 10 and 100 mm and/or whose equivalentdiameter is between 10 and 100 mm.
 3. The block as claimed in claim 1,whose porosity is less than or equal to 2%.
 4. The block as claimed inclaim 1, wherein the composition of the gas-generating pyrotechnicmonolithic block contains said guanidine nitrate and said basic coppernitrate in a ratio, R, between 8.5 and 15 (8.5≦R≦15).
 5. The block asclaimed in claim 1, wherein said at least one inorganic titanateconsists of at least one inorganic titanate selected from the groupconsisting of metal titanates and alkaline-earth titanates.
 6. The blockas claimed in claim 1, wherein said at least one inorganic titanateconsists of strontium titanate (SrTiO₃) and/or calcium titanate (CaTiO₃)and/or aluminum titanate (Al₂TiO₅).
 7. The block as claimed in claim 1,wherein said guanidine nitrate, basic copper nitrate and at least oneinorganic titanate represent at least 97 wt. % of its weight.
 8. Theblock as claimed in claim 1, wherein the composition of thegas-generating pyrotechnic monolithic block contains, in addition tosaid guanidine nitrate, basic copper nitrate and at least one inorganictitanate, at least one processing additive, in a proportion by weightnot exceeding 1%.
 9. The block as claimed in claim 1, wherein thecomposition of the gas-generating pyrotechnic monolithic block contains,in addition to said guanidine nitrate, basic copper nitrate and at leastone inorganic titanate, at least one binder or at least one flux, in aproportion by weight not exceeding 5%.
 10. The block as claimed in claim1, wherein the composition of the gas-generating pyrotechnic monolithicblock contains, for 100% of its weight: said guanidine nitrate, saidbasic copper nitrate, said at least one inorganic titanate, and at leastone processing additive.
 11. The block as claimed in claim 1, whereinthe composition of the gas-generating pyrotechnic monolithic blockcontains, for 100% of its weight: said guanidine nitrate, said basiccopper nitrate, said at least one inorganic titanate, at least oneprocessing additive, and at least one binder or at least one flux.
 12. Amethod for obtaining a gas-generating pyrotechnic monolithic block, ofsubstantially cylindrical shape, as claimed in claim 1, wherein themethod consists of a dry process or a wet process.
 13. The method asclaimed in claim 12, wherein the method consists of a dry process, whichcomprises: compressing a pulverulent mixture containing said guanidinenitrate, said basic copper nitrate, said at least one inorganictitanate, at least one processing additive and optionally at least oneflux; or compacting a pulverulent mixture containing said guanidinenitrate, said basic copper nitrate, at least one processing additive andoptionally at least one melting agent for obtaining a compactedmaterial, followed by granulating said compacted material to obtaingranules, followed by compressing said granules; said at least oneinorganic titanate being added to the pulverulent mixture to becompacted and/or to the granules to be compressed.
 14. The method asclaimed in claim 12, wherein the method consists of a wet process, whichcomprises: extruding a paste containing said guanidine nitrate, saidbasic copper nitrate, said at least one inorganic titanate, at least oneprocessing additive, at least one binder and a solvent; or preparing anaqueous solution containing at least said guanidine nitrate, optionallysuspending at least basic copper nitrate in said aqueous solution,obtaining a powder by spray-drying said solution or suspension, ifnecessary adding complementary constituent(s) of said block to saidpowder and shaping the powder, optionally added with said complementaryconstituent(s), containing all the constituents of said block; said atleast one inorganic titanate being added to the solution or suspensionto be spray-dried and/or to the spray-dried powder.
 15. A gas generator,containing a gas-generating solid pyrotechnic charge, wherein saidcharge contains at least one block as claimed in claim
 1. 16. The blockas claimed in claim 1, wherein the composition of the gas-generatingpyrotechnic monolithic block contains said guanidine nitrate and saidbasic copper nitrate in a ratio, R, between 8.5 and 12 (8.5≦R≦12). 17.The block as claimed in claim 1, wherein said guanidine nitrate, basiccopper nitrate and at least one inorganic titanate represent at least 99wt. % of its weight.
 18. A method as claimed in claim 12, wherein saidmethod consists of a dry process.
 19. A gas generator, containing agas-generating solid pyrotechnic charge, wherein said charge contains atleast one block obtained according to the method of claim 12.